Integrated circuits have become the technology of choice for performing electronic functions. The downscaling of minimum device geometries has provided for increases in the functional density of electronic circuits. The development of nanoelectronic devices has allowed for the continuing increase in functional density of integrated electronic systems beyond the currently perceived limits for conventional electron devices. The term "nanoelectronics" refers to an integrated circuit technology which permits downscaling of minimum circuit geometries to on the order of 0.01 microns.
Physical principles by which conventional transistors operate are no longer utilized at the nanoelectronic size scale. In this range of dimensions, the behavior of electrons in semiconductors can no longer be understood by thinking of electrons as particles, but the wave-like nature of electrons must be invoked. Device physicists call this the "quantum regime" and it requires a different mathematical description of electron behavior. The most important quantum phenomena for the development of quantum devices is the ability of an electron to "tunnel" through a potential energy barrier, rather than having to go over it as would a classical particle. Another important quantum phenomenon is quantum size effects or confinement effects. If an electron moving through a semiconductor is thought of as a Bloch wave, a quantum well within a device can be structured to have a dimension less than the coherence length of the Bloch wave involved. At the characteristic length scales, the electrons can then resonate due to the constructive interference of forward and backward Bloch waves, and steady state tunneling current is substantially reinforced, like the sound from a resonating organ pipe. These quantum confinement effects can be observed in an electronic device when a dimension of a structure within the device is on the order of 100 Angstroms. The device is thus said to provide charge carrier quantization in the particular dimension.
When a dimension of a semiconductor region within a quantum device reaches approximately 100 Angstroms, the conduction band characteristics change. In an ordinary semiconductor structure having conventional geometries of substantially greater than 100 Angstroms, the conduction band contains a continuous spectrum of possible energy levels for electrons to occupy. As quantum size effects or confinement effects become apparent, this continuous spectrum of energy levels divides into defined subbands of allowed energies with gaps separating the subbands. The principles of a resonant tunneling diode use these allowed energy bands to switch current on and off by adjusting the bias across the quantum well.
The energy subbands and gaps will appear if a single dimension of the quantum well is on the order of 100 Angstroms. If two dimensions of the quantum well are on the order of 100 Angstroms with the third dimension being substantially greater than 100 Angstroms, the device is commonly referred to as a quantum wire. The quantum wire will have narrower and different subbands than the quantum well which has only a single quantized dimension. If all three dimensions of the quantum well are on the order of 100 Angstroms or less, the quantum well is commonly referred to as a quantum dot structure. In a quantum dot structure, the energy subbands will further subdivide and become discrete energy states.
Prior art quantum devices have used quantum wells having defined dimensions and have created diode structures which will change conduction characteristics as the bias voltage across the quantum wells is altered. While these designs can produce efficient and highly conductive devices, these devices do not operate in a similar manner to the traditional three terminal switching device such as the common field effect transistor. Accordingly, a need has arisen for a quantum effect device which utilizes the change in the energy levels of the conduction band through the effective dimensional modulation of the quantum well of the device to provide a three terminal switching device.